The present invention relates to a charged beam radiation apparatus and, more particularly, to a charged beam radiation apparatus such as a scanning electron microscope used in a system for measuring, with a charged beam, micropattern sizes of electronic devices such as VLSIs during their fabrication, or in a system for testing these devices in a noncontact manner.
It is very important to control sizes of resist films and wiring layers in the VLSI fabrication process. Along with the development of micropatterning, a system for measuring pattern sizes using a scanning electron microscope has been used. Such a system is described in Japanese Patent Publication No. 59-761 published on Jan. 9, 1984. According to this system, two movable position markers are displayed on an image display cathode-ray tube (CRT) by superposing them on a sample scanned image or a secondary electron signal waveform. The size of a sample image or the like is calculated by the distance between the markers. In this case, an operator must select a target pattern to be measured while observing a scanned image, and set an electron beam in a line scanning mode. The two markers superposed on the resultant secondary electron signal waveform are then displayed on the CRT screen. After the operator adjusts the marker positions to a position to be subjected to measurement, the size is calculated according to the marker distance and a magnification. Therefore, the operator must designate the measuring point for each measurement. Because of this, a plurality of points cannot be automatically and continuously measured.
In order to measure a wiring width upon automatic setting of a slice level, a secondary electron signal can be converted to a digital signal, and a wiring portion can be selected according to the digital signal and then measured. In size measurement, however, the numbers of secondary electrons, depending on the kind of material, are measured without application of an external voltage. If line scanning is performed on materials having identical secondary electron emission ratios or if a charge-up phenomenon tends to occur due to radiation conditions, an edge of an underlying material may be erroneously detected as the edge of a wiring portion. For example, when the charge-up phenomenon occurs and a secondary electron signal waveform as shown in FIG. 1(a) is obtained, its digitized signal waveform is as shown in FIG. 1(b). Although an actual wiring width is given as L, it is erroneously detected as l. Thus, a distance (incorrect width) different from a target distance is measured.